Structural epicardial disease and microvascular function are determinants of an abnormal longitudinal myocardial blood flow difference in cardiovascular risk individuals as determined with PET/CT

Abstract

Background. The aim of this study was to determine whether epicardial structural disease may affect the manifestation of a longitudinal decrease in myocardial blood flow (MBF) or MBF difference during hyperemia in cardiovascular risk individuals, and its dependency on the flow increase.Methods and Results. In 54 cardiovascular risk individuals (at risk) and in 26 healthy controls, MBF was measured with 13 N-ammonia and PET/CT in mL/g/min at rest and during dipyridamole stimulation. Computed tomography coronary angiography (CTA) was performed using a 64-slice CT of a PET/CT system. Absolute MBFs during dipyridamole stimulation were mildly lower in the mid-distal than in the mid-LV myocardium in controls (2.20 ± .51 vs 2.29 ± .51, P < .0001), while it was more pronounced in at risk with normal and abnormal CTA (1.56 ± .42 vs 1.91 ± .46 and 1.18 ± .34 vs 1.51 ± .40 mL/g/min, respectively, P < .0001), resulting in a longitudinal MBF difference that was highest in at risk with normal CTA, intermediate in at risk abnormal CTA, and lowest in controls (.35 ± .16 and .22 ± .09 vs .09 ± .04 mL/g/min, respectively, P < .0001). On multivariate analysis, log-CCS and mid-LV hyperemic MBF increase, indicative of microvascular function, were independent predictors of the observed longitudinal MBF difference (P £ .004 by ANOVA).Conclusions. Epicardial structural disease and microvascular function are important determinants of an abnormal longitudinal MBF difference as determined with PET/CT. (J Nucl Cardiol 2010;17:1023-33.)

Positron Emission Tomography-Determined Hyperemic Flow, Myocardial Flow Reserve, and Flow Gradient—Quo Vadis?

“…Some help may come from a more specific flow parameter such as a longitudinal decline in flow from the base to the apex of the heart or so-called hyperemic longitudinal MBF gradient to identify and characterize flow-limiting CAD lesions (24–26, 64–66). A longitudinal MBF gradient of the LV is assumed to be induced by CAD caused increases in epicardial resistance during hyperemic coronary flows (67–69).…”

“…In the normal coronary circulation, an increase in coronary flow and thus velocity due to a metabolic-mediated vasodilation in the microcirculation in response to an increase in oxygen demand induces a flow-mediated vasodilation of the epicardial artery that again reduces the velocity-induced increase in resistance in order to ascertain a low coronary resistance at the level of the epicardial conductance system (64, 75–77). The presence of diffuse CAD and/or advanced focal CAD lesion, however, will prevent or reduce an appropriate flow-induced and endothelium-dependent vasodilation of the epicardial artery and the additional intraluminal obstruction will cause an increase in epicardial resistance accompanied by a continuous decrease in intracoronary pressure from proximal-to-distal (68) that may manifest as longitudinal decrease in MBF or MBF gradient (25, 26, 66, 71, 78). Thus, the identification and characterization of a hyperemic longitudinal MBF gradient with PET/CT could indeed evolve to a unique and specific flow parameter to signify flow-limiting CAD lesions.…”

Mitochondrial-Targeted Molecular Imaging in Cardiac Disease

“…In contrast, PET imaging provides robust and sensitive measurements of MPI; it offers an excellent resolution, high sensitivity, lower tissue attenuation, and semiquantification or absolute quantification of MBF [6]. Many findings suggest using PET tracers because of their sensitivity and dynamic-imaging capabilities [7, 8] for myocardial function and viability detection [9, 10]. PET imaging is very complicated for nuclear cardiologists in contrast to SPECT perfusion imaging, which is still the most commonly used nuclear imaging technique in clinical practice.…”

Artifact-free quantitative cardiovascular PET/MR imaging: An impossible dream?

“…13,14 Caution shall still prevail as more systematic comparisons between cardiac PET/MRI and PET/CT are needed especially using routine nuclear cardiology tools, such as semi-quantitative polar maps, absolute flow comparison, and regional comparisons as well. 15,16 Therefore, caution speaks toward keeping routine cardiac PET on PET/CT scanners, where optimal quantification can be guaranteed and toward keeping the search for better attenuation compensation algorithms on hybrid PET/MRI systems.…”